Literature Review of the Effects of Age on Second Language Acquisition
第二言語習得における年齢の影響に関する文献レビュー
N o b u e I N O U E
井 上 信 恵
Abstract
This literature review aims to explore whether age influences learners＇ second language acquisition. A significant observation is that the critical period hypothesis (CPH) which suggests that biologically endowed mechanisms to learn a language are only available during a critical period (CP) (until around puberty), has resulted mainly in three scholarly positions: (1) Adults will never reach native-level fluency because, unlike children, they do not have access to innate biological mechanisms such as universal grammar that is necessary to be proficient in a language; (2) adults are still capable of mastering a language because they also have access to universal grammar, and any evidence concerning the CPH is contradictory; how learners succeed in second language acquisition is variable and is affected by factors other than age; and (3) there is no universal CP, and each linguistic domain is affected differently—in particular, it is possible that adults can also reach a very high level of proficiency except in the area of phonology. The findings show that the relevant scholars＇ views are inconclusive and that the relationship between age and second language acquisition is still unclear.
Keywords: critical period, CP, critical hypothesis period, CPH, age effects on languages
本レビューは、年齢が第二言語習得へ影響を与えるかについて調査を行うことを目的としている。 レビューの結果、生物学的上の言語習得機能はcritical period（およそ思春期まで）の間のみ有効で ある、というCritical Period Hypothesisには、主に三つの学問的見解があることが明らかとなった。 （１）子供と異なり、critical periodを過ぎた大人は、言語習得に必要なuniversal grammarといっ た生来の生物学的機能を使用できないため、ネイティブレベルの流暢さを身につけることが決して できない。（２）大人もuniversal grammarを利用できること、またcritical period hypothesisに関 する根拠は矛盾していることから、大人でも言語を極めることができる。また、言語習得の度合い は学習者によって異なり、年齢以外の要因に影響される。（３）均一のcritical periodは存在せず、 各言語領域によって影響が異なる。とりわけ、phonology以外の分野であれば、大人も非常に高度 な語学力を身につけられる可能性がある。これらの結果から、本分野の学問的見解は様々であり、 年齢と第二言語習得との関係性は未知数であるといえる。 キーワード：クリティカルピリオド、クリティカルピリオド仮説、年齢と第二言語、年齢と第二言語習得、 年齢と第二言語習得の関係
Literature Review of the Effects of Age on Second Language Acquisition
It is generally believed that young children possess some inherent advantage in learning languages and find it easier to gain mastery over a second language (L2) compared with adults (Gass, Behney, & Plonsky, 2013; Johnstone, 2002; Schmid, 2016). This popular opinion is often expressed by the familiar mantra that, unlike adults, children immersed in a foreign language ‘soak it up like a sponge＇ because they are far less inhibited and far more open and receptive (Johnstone, 2002; Schmid, 2016). In other words, childhood is considered a critical period (CP) for language learning (usually assumed to last until puberty), during which the human brain is specifically sensitive to linguistic input (Schmid, 2016). This ‘the younger, the better＇ argument has led to the introduction of L2 learning into the school curriculum at an early age (Thornbury, 2006). However, as Thornbury (2006) noted, “the precise relationship between age and second language learning remains unresolved and controversial” (p.10); researchers have failed to reach an agreement on the function of age and maturation in second language acquisition (SLA) despite the vast amount of relevant research (Schouten, 2009). This brings me to the question of whether it is actually too late for older learners to gain mastery of a foreign language.
I teach English at a Japanese university whose student body includes a large number of vocational high-school graduates who mainly took non-academic courses and had few opportunities to learn English. Due to their educational backgrounds, the university＇s placement test results have shown that they belong somewhere between levels A1 and A2, or even below the A1 level, as per the Common European Framework of Reference for Languages (CEFR) standard that shows language ability. Nevertheless, several students are really motivated to study English and are eager to improve their language skills by taking complete advantage of the university＇s English courses. If age actually affects language abilities, I need to develop the curriculum in focusing on creating an optimum learning environment for those who did not take full advantage of an opportunity to start studying English at an early age.
The purpose of this paper, therefore, is twofold: first, to investigate whether age actually affects L2 learners＇ language abilities and second, to find out how significantly age influences learners＇ level of L2 attainment. To fulfil the main objectives, an overview of the theories regarding CP will be summarised first, and then several views about the effects of age on SLA will be explored. Lastly, there will be a brief attempt to identify the possible implications of an ideal English curriculum for adults.
Literature Review
Critical Period Hypothesis
The concept of CP was first proposed and introduced by Penfield and Roberts (1959) in their book Speech and Brain Mechanisms (Marinova-Todd, 2003; Muñoz, 2006; Vanhove, 2013). As for
learning languages, the human brain becomes progressively stiff after nine years of age, and achieving a good result is difficult in the second decade of life because it is unphysiological (Penfield & Roberts, 1959). This belief was refined and popularised by Lenneberg, who is generally acknowledged as the father of the critical period hypothesis (CPH) (Singleton, 2003; Vanhove, 2013; Vijaykumar & Vijay, 2013); in his 1967 book Biological Foundations of Language, the ‘onset of speech＇ is proposed, which starts roughly at age two when a certain level of physical maturation and growth has been attained to develop language and the brain functions in a flexible manner (Lenneberg, 1967). As a result, speech and language can be smoothly elaborated between three years of age and the early teens, whereas such capacity to learn language deteriorates after puberty (Lenneberg, 1967).
To summarise, the CPH refers to the idea that biologically endowed mechanisms are operational during a certain period and so language acquisition would be severely hampered past a certain age (VanPatten & Benati, 2010). Although the CPH is directly concerned with first language acquisition (FLA) and Lenneberg did not mention much about SLA, his CPH concept has guided a great deal of SLA research and age effects on SLA have caught more scholarly attention for almost four decades (Krashen, 1975; Moyer, 2004; Vanhove, 2013; VanPatten & Benati,2010; Vijaykumar & Vijay, 2013).
In fact, “a number of researchers in recent years have affirmed that there is a maturational limit (usually set around puberty) beyond which it is simply impossible to acquire an L2 (or certain aspects thereof) to native levels” (Singleton, 2003, p. 8). More specifically, Singleton (2003) proposed three commonly advanced views concerning the CPH on the basis of researchers＇ theoretical predispositions. The first view is that L2 learners are no longer capable of attaining native-level proficiency after a certain age of maturation (Singleton; 2003); the second view is that L2 learners past puberty require more effort than before (Singleton; 2003); and the third view is that there may be fundamental differences between children and adults in terms of language acquisition or language process mechanisms and hence, L2 learners are no longer subserved by the same mechanisms as children after a certain age of maturation (Singleton; 2003).
In contrast, there are a number of scholars rejecting the CP itself, who argue that FLA and SLA are fundamentally similar because both use the same linguistic mechanisms for acquisition, which indicates that L2 learners can obtain native-like ability even after puberty (Richards & Schmidt, 2010; VanPatten & Benati, 2010). Actually, linguistic researchers have demonstrated that as per experimental research, adults can outperform young children under controlled conditions in both formal and informal learning situations (Merritt, 2013; McLaughlin, 1992). Nevertheless, Moyer (2004) has added that although adults past the age of 15 are capable of a
high level of mastery, it is unclear whether native-level production is impossible for adults, or just improbable for them, due to physiological or psychological hindrance. As a result, “recent studies have taken a new approach to the CPH by either narrowing its focus, expanding it parameters, or suggesting that it be considered in conjunction with other important factors” (Schouten, 2009, p. 14).
Several scholars also maintain that not all (or none of the) components of the linguistic system have CP/SPs１ and so the construct of a monolithic CP is not appropriate (Rothman, 2008;
VanPatten & Benati, 2010). They believe that there is no universal CP, but there are different phases of offsets for specific linguistic sub-modules, or perhaps CPs for certain dimensions of language but not for others (Rothman, 2008; VanPatten & Benati, 2010).
To summarise, there are mainly three perspectives taken by scholars on the CPH for SLA: ‘there is a CP＇, ‘there is no CP＇ and ‘there are CPs for some things＇ (VanPatten & Benati, 2010).
The following subsections explain the details on each perspective.
There is a CP
The major difference between children and adults can be summarised in Bley-Vroman＇s (1989) Fundamental Difference Hypothesis (FDH) which suggests that the inborn mechanism of childhood is no longer available in adulthood (Gass et al., 2013; Muñoz, 2006; VanPatten & Benati, 2010). Bley-Vroman (1989) argued that adults learn language differently because they already have knowledge of at least one language and the function of their innate domain-specific acquisition system is filled by this native language knowledge and general abstract problem-solving system. In contrast, young children pick up a language naturally and unconsciously because they still utilise their innate FLA strategies (Dunn, n.d.).
Thornbury (2006) also mentioned that some theorists propose the existence of an innate language acquisition faculty as FLA is always successful despite the widely different exposure provided to children. This is supported by the universal grammar (UG) theory adopted by Noam Chomsky (Thornbury, 2006); Chomsky (2010) defined UG as the biological endowment that makes it possible for a grammar of the required sort to develop in humans and is considered a function that maps a body of experience into a particular grammar. Although the theory is intended for FLA, proponents of the CPH claim that L2 learners past a certain age have no access to UG (Thornbury, 2006). This basic biological assumption suggests that those who have no access to UG learn L2 differently from L1 and thus, adults cannot pick up a language as children can (Marinova-Todd, 2003; Thornbury, 2006). In other words, the lack of access to UG explains the reason why SLA is not as successful in adults as in children (Muñoz, 2006).
As for the best age to learn a language, Moyer (2004) explained that the age of onset (AO) is typically cited as the critical factor in the debate on differences in L2 attainment among children
and adults. CPH supporters believe that late learners (post puberty) are deficient in their ultimate L2 attainment, whereas early learners (before puberty) perform in a native-like fashion (Schouten, 2009). This is demonstrated by Patkowski (1980) who found that those who arrived in the U.S. as immigrants before the age of 15 (n = 33) mostly outperformed those who arrived later (after 15 years of age) (n = 34) in the acquisition of syntax in English, while the years of residence in the U.S. and hours of informal and formal exposure to English had little effect on the subjects＇ abilities.２
Furthermore, some have proposed that, in regards to identifying a CP, there is a steady gradual decline in language learning without sharp breaks (Richards & Schmidt, 2010; VanPatten & Benati, 2010). Rather, they note that the earlier the age of acquisition, the more likely they are to be close to native-likeness (VanPatten & Benati, 2010). For example, Johnson and Newport (1989) tested the knowledge of English syntax and the morphology of Chinese and Korean speakers (N = 46) who had moved to the U.S. (AO = 3–39). The results revealed that those who arrived before the age of seven reached native performance, whereas there was a linear decline in performance through puberty for those who arrived after the age of seven, and those who arrived after puberty performed much more poorly than the younger counterparts (Johnson & Newport, 1989). Thus, Johnson and Newport concluded that a small decline in language abilities occurs well before puberty and another bigger change occurs around puberty. According to Qingxin (2012), this is one of the studies that supports the existence of a CP for SLA and still receives much attention today.
There is no CP
Galván García (2012) and Richards and Schmidt (2010) suggested that the CPH has been questioned by many researchers in recent years and some theorise that there is no CP at all and so SLA is absolutely possible after puberty. Some scholars offer evidence against a CP to prove that adults have access to UG as well as linguistic mechanisms that are present in FLA, while others reanalyse the data from those who have advocated a CPH in order to show how the data can be interpreted in a different way (VanPatten & Benati, 2010).
Primarily, a number of scholars reject the CP by arguing that adults have access to UG as well as the linguistic mechanisms guiding acquisition that are present in FLA (VanPatten & Benati, 2010). Actually, White and Genesee (1996) found that although younger learners (AO = seven or below) generally achieved a more near-native proficiency than older starters, some adults (less than one third) (AO = post 16) were able to discriminate grammatical and ungrammatical English sentences, thus showing a native-like accuracy (White & Genesee, 1996).３
In addition, even though the UG theory provides an attractive solution to some basic conundrums of language, critics of the CPH argue that CPH supporters rely on an elusive
faculty whose existence has not been proved (Thornbury, 2006). Some claim that L2 learners have complete access to UG and hence, native-like proficiency is achievable, while others claim that UG is no longer accessible after a certain age and those who must rely on general learning strategies to learn a language cannot achieve native-like proficiency (Thornbury, 2006). Thus, research evidence has been diverse and inconclusive and the role of UG in SLA is much less clear and not uniformly accepted (Marinova-Todd, 2003; Thornbury, 2006).
Another thing to consider is that learners vary in how successful they are in SLA in terms of the speed of acquisition as well as their ultimate level of achievement (Ellis, 1994). In particular, adults＇ SLA show various degrees of variability, and there have never been serious theories on adults' SLA claiming that the overall learning process and outcomes are identical (Rothman, 2008). In fact, Johnson and Newport (1989) identified distinguished individual differences in the performance among those who arrived in the U.S. after 17 years of age, which was not found in those who arrived before that age. Therefore, Johnson and Newport acknowledged that while young learners are uniformly successful in SLA, any proposed mechanism accounting for L2 performance is not correlated with age in the case of adult learners.
Marinova-Todd (2003) also noted that even though older learners typically achieve more limited levels of L2 success, some individuals achieve native-like competence. For instance, it is likely that older learners have more difficulty with oral fluency and accent than younger learners (Cummins,1980), but McLaughlin (1992) pointed out that some studies show better results for older learners. This was proven by Nikolov (2000) who conducted case studies among 33 learners of English and Hungarian aged 20–70 years (AO = 15 or later).４ The results showed
that two subjects (Bulgarian and German/English) were mostly mistaken for Hungarians and one Hungarian was considered a native English speaker overall (Nikolov, 2000); furthermore, four subjects (English, Finnish, Russian and Polish) were often or sometimes mistaken for Hungarians and four Hungarians were often mistaken for English native speakers (Nikolov, 2000). These findings indicate that the mechanisms behind late learners＇ attainment are variable and complex, leading to great variation in outcomes (Moyer, 2004).
Furthermore, SLA reflects individual variations influenced by factors such as learning circumstances, experiences and socio-psychological factors (Moyer, 2004). According to Midgley (2017), young children benefit the most from a language immersion environment, and early teens make the most out of classroom instruction by maximising the balance between meta-cognitive skill development and years of classroom learning. This implies that children＇s SLA is further facilitated by social factors such as a nurturing environment, simplified input, educational opportunities and cooperative peers (Bialystok & Hakuta, 1999). Therefore, Galván García (2012) argued that ‘the younger the better＇ argument, which suggests that anyone older
than a teenager fails to succeed in SLA, reflects psychological and social factors; and linguistic competence would not be subject to a biological decline (White & Genesee, 1996). For these reasons, Midgley contended that the best age for SLA can vary depending on how the language is learned.
There are CPs for some things
Recent studies have shown that the CP would influence each aspect of language differently (Humanes, 2012). Although there is considerable disagreement about which modules are affected by the CP (Rothman, 2008), efforts have been made in recent years to identify the linguistic areas affected by age (Slabakova, 2006). In other words, there may be several cut-off points depending on different language aspects (Humanes, 2012). For instance, Long (1990) suggested that learners should be exposed to L2 before six years of age (around 12 for some) in order to attain native-like phonological abilities, whereas L2 attainments in morphology and syntax only seem to be possible before 15 years of age and the exposure needs to occur somewhere between those ages for other domains. Long pointed out that, even though some late L2 learners reach a very high level of proficiency, the apparent inability of late starters to attain native-like proficiency suggests that there is/are one or more CPs for SLA.
Herschensohn (2000), however, suggested that the inability of adults to master a language is proverbial and that the incompleteness of SLA and its reliance on explicit instruction are characteristics that seem to eclipse certain adults＇ L2 competency. Actually, some scholars argue that there is probably no age limit to acquire vocabulary (Richards & Schmidt, 2010); Humanes (2012) explained that vocabulary is the least affected area of language and older learners are able to acquire new words just like younger learners. Slabakova (2006) also suggested that there are differential age-related effects for specific parts of grammatical competence, which can be united under the label Multiple CPH. Some scholars believe that L2 learners still have access to the principles of UG, but new parameters are not available to them (VanPatten & Benati, 2010).５ Such researchers contend that principles do not disappear once the L2 is set and remain
with speakers for their entire lives, yet other values are lost and cannot be retrieved once the parameters are set for L1 values (VanPatten & Benati, 2010). Thus, it is believed that there is no CP for principles, but there is a CP for parameters, beyond which the resetting of parameters is impaired (VanPatten & Benati, 2010).
Rothman (2008) also suggested that any CPH claiming that adults lose the ability to acquire syntax like children acquire holds that target syntactic properties are represented differently in adults＇ L2 mental grammar because adults explicitly learn L2 knowledge of properties that are different from L1. Within the framework of UG, it is only positive evidence that can be used by the language learning mechanism (VanPatten & Benati, 2010). Positive evidence refers to the
input that learners hear/read from the communicative environment and comprises a limited set of well-formed L2 utterances that actually occur, which tells learners that something is possible in the L2 without direct negative feedback such as error correction (Gass et al., 2013; Richards & Schmidt, 2010; VanPatten & Benati, 2010). This term stands in contrast to negative evidence, which comprises information concerning incorrectness and tells the learner that his/her utterance is deviant and not possible with regard to the L2 norms (Gass et al., 2013; Richards & Schmidt, 2010; VanPatten & Benati, 2010).
These views are implicated in the poverty of stimulus (POS) which suggests that learners only get positive evidence in the input and that the input does not provide learners with negative evidence on the grammatical and syntactic knowledge of the language (Richards & Schmidt, 2010; VanPatten & Benati, 2010). POS is the bedrock of UG outlined by Noam Chomsky, which indicates that humans are innately and uniquely endowed with a language instinct and know more about what can and cannot be done in the language than they could have learned from the input alone or the data provided to them (Gass et al., 2013; Thornbury, 2015; VanPatten & Benati, 2010). In other words, the definition indicates that true POS properties are not transferrable from L1 and hence, late learners can be shown to acquire new L2 POS morphosyntactic and semantic properties (Rothman, 2008). Actually, a research by Song and Schwartz (2009) showed that adults can overcome L2 POS problems related to syntax and are constrained by UG like children. They explained that English speakers face learnability issues in the acquisition of the two properties of Korean wh-constructions with negative polarity items (NPIs) due to the grammatical differences between English and Korean, and tested adults (n = 15) and children (n = 10) who had been learning Korean in a classroom setting in Hawai＇i.６
The results showed that highly proficient learners achieved native-like responses concerning the two properties and that adults and children in the high-proficiency group showed the same developmental route (Song & Schwartz, 2009).
When it comes to phonology, however, younger learners can sound like native speakers, while older learners retain a noticeable foreign accent even if they attain fluency (Humanes, 2012; Moyer. 2004). The view is contradictory to Nikolov＇s (2000) findings; and yet, Merritt (2013) explained that the brain is more open to new sounds and patterns in pre-adolescence and thus, younger learners are more skilled at identifying subtle differences in sounds. In addition, Lightbown and Spada (2013) contended that L1 plays an important role for L2 pronunciation; as pronunciation involves motor patterns that have been fossilised in L1, altering such patterns are difficult after a certain age due to the nature of the neurophysiological mechanisms (McLaughlin, 1992). Therefore, Moyer (2004) pointed out that late learners require great effort, a desire to sound native and optimal experience in the language in order to get beyond a non-native accent.
Certainly, Lightbown and Spada (2013) mentioned that there is theoretical and empirical work that helps in understanding the processes involved in phonological development such as contrastive analysis (CA); the CA refers to the comparison of the linguistic systems of two languages and helps explain L1＇s influence on L2＇s pronunciation (Lightbown & Spada, 2013; Richards & Schmidt, 2010). It is believed that “CA＇s most successful predictions are in the area of phonology, where the influence of the L1 is more in evidence than it is in grammar learning” (Thornbury, 2006, p. 53).７
Discussion and Conclusion
The widely held view that children are better at learning a language than adults owing to their innate biological mechanisms is supported by the CPH, which has led to various views about whether the CPH applies to SLA. On the one hand, CPH advocates argue that adults past puberty will never reach native-level, or some believe that one＇s language abilities decrease with age without a particular cut-off point. On the other hand, CPH opponents suggest that adults are still capable of mastering a high level of proficiency; they appear to recognise younger learners＇ advantages over adults, yet they argue that factors other than age might influence SLA. In addition, several scholars maintain that there is/are CPs for each linguistic domain and others argue that there are CPs only for certain areas. In this regard, the relationship between age and SLA is inconclusive and still unclear.
Nevertheless, this literature review has shown that the notion of ‘the younger the better＇ is not always true. Rather, there are numerous cases of successful language learners who began learning late in life (Ghazali, 2006) as noted earlier. In fact, the Polish-born writer Joseph Conrad, who learned English at 18, was able to write fluently and creatively in English and is generally regarded as a master prose stylist, which implies that L2 learners may succeed in SLA, at least in certain domains such as vocabulary or syntax (Klein, 1986; Herschensohn, 2000; Scovel, 1969). Unfortunately, Joseph Conrad failed to acquire an authentic English pronunciation and continued to speak it with a strong Polish accent (Bongaerts, Planken. & Schils, 1995; Klein, 1986). Similarly, the former Secretary of State Henry Kissinger, who was born in 1923 in Germany and immigrated to the U.S. in 1938, is said to have a noticeable German accent, even though he was fluent enough to negotiate subtle and difficult diplomatic relations (Ghazali, 2006; Herschensohn, 2000; The Editors of Encyclopædia Britannica). This indicates that the CPH does not hold true in cases of successful adult learners, except in the area of pronunciation. In this regard, I would take the third position in this paper (＇There are CPs for some things＇). Merritt (2013) noted that pronunciation is not actually an indicator of fluency and an accent should not impede communication unless the pronunciation is extremely
poor. In other words, adult learners are capable of being ‘fluent＇ in a foreign language.
In actuality, adults have a more developed understanding of how language works because they already have pre-existing language knowledge such as grammar and a greater conceptual understanding to deduct and apply language rules (Merritt, 2013). Moreover, adults have access to a wider range of topics, enabling more complicated communication (Merritt, 2013). However, Merritt (2013) also pointed out that these higher expectations lead to adults＇ typical inhibitions. Moreover, Galván García (2012) noted that adult learners can be more anxious and under-confident due to their previous failure and the conscious or unconscious acceptance of the stereotype of adults＇ diminishing learning power with age.
Last but not least, this paper did not explore what kind of curriculum would be appropriate for older beginners because it was not the focus of this review. However, I would like to point out some significant implications for future research. Galván García (2012) suggested that L2 programmers should be developed in such a way that they reduce anxiety and build self-confidence because affective factors including motivation, anxiety and self-self-confidence affect a person＇s attitude towards L2 learning, and anxiety might be the reason why older learners are less successful at school-based language learning than middle-school learners. Merritt (2013) also argued that adults benefit from developed language programmes in classroom just like children, while adults studying at home without others＇ support are unlikely to achieve language learning success due to its unstructured nature. In contrast, Midgley (2017) suggested that self-directed learning is more beneficial for adults because a range of skills including the ability to remain self-motivated are not usually developed until adulthood. Due to lack of available data, it is difficult to designate one of the views as correct, yet these suggestions imply that adult learners are capable of overcoming their difficulties and of achieving native-like proficiency if they are provided with an optimum learning environment.
To conclude, there is no universal agreement as to whether age affects SLA, but some studies indicate that adult learners have the potential for successful SLA, as mentioned before. As a university teacher of those who failed to learn English willingly before college, I would like to keep trying to find the best curriculum for older beginners.
Footnotes
１ Long (1990) noted that most ethological and psychological literature uses sensitive period (SP) and CP interchangeably, although there is a growing preference for SP; the SP is a weaker and less restrictive version of the CP, allowing for more variation in ultimate attainment and variation of SLA (VanPatten & Benati, 2010). As this paper focuses on the CPH, I use CP for the sake of convenience.
２ The native languages of the subjects (N = 67) included Spanish (24 cases), Polish (17 cases) and Chinese (nine cases), as well as French, Haitian Creole, Czech, Arabic, Turkish, Rumanian, Hebrew, Bengali, Russian, Italian and Serbo-Croatian (three or fewer cases each) (Patkowski, 1980).
３ The majority of the subjects (n = 58) among the total 89 subjects were born and raised in Quebec, Canada, where French was the only official language (White & Genesee, 1996). They were separated into four age groups (0–7 years, 8–11 years, 12–15 years, and 16+) on the basis of their initial exposure to English excluding ESL instruction (White & Genesee, 1996).
４ The subjects consisted of 20 learners with different L1 (Bulgarian, English, German/English, Laotian, Finnish, Polish, Russian and Spanish) learning Hungarian and 13 Hungarians studying English (Nikolov, 2000).
５ Within Chomsky’s UG, there are universal ‘principles’ which apply to all languages as well as special conditions or rules called ‘parameters’ that may vary from one language to another (Richards & Schmidt, 2010; VanPatten & Benati, 2010).
６ The first property (intervention effect) is not a characteristic of English because scrambling of the object wh-phrase becomes obligatory for wh-object questions with a NPI only in Korean, while the second property is concerned with Korean’s interpretation differences, i.e. the ambiguity between wh-question and yes/no-question interpretation of both non-scrambled (SOV) and scrambled (OSV) word orders (Song & Schwartz, 2009).
７ It is worthwhile to mention that the CA declined during the 1970s because interference was replaced by other theories and that the CA has been applied to other linguistic domains such as discourse analysis recently (Richards & Schmidt, 2010).
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